This invention relates to a method and apparatus for detecting contaminants dissolved in an alcohol-gasoline fuel mixture that is delivered to an internal combustion engine, and more particularly, to a method and apparatus for providing an indication of substandard fuel quality when the degree of contamination reaches an unacceptable level.
Alcohols such as ethanol or methanol have been proposed as possible alternatives to gasoline for fueling conventional internal combustion engines. Although it is possible to operate an engine on a pure alcohol fuel, gasoline is generally mixed with the alcohol to increase the fuel vapor pressure and improve engine starting and warm-up operation.
For an engine capable of operating on a variable alcohol-gasoline fuel mixture, it is necessary to know the relative concentrations of alcohol and gasoline in the fuel to effectively control the engine air-fuel ratio for optimal combustion. It is well known that the dielectric constant of such a fuel is related to the proportion of alcohol to gasoline in the mixture. In the prior art, this relationship has been utilized for determining the composition of variable alcohol-gasoline fuel mixtures. For example, U.S. Pat. No. 4,915,084 issued to E. V. Gonze on Apr. 10, 1990, which has been assigned to the assignee of the present application, discloses a capacitive sensor positioned in an engine fuel supply line and a capacitance measuring circuit for determining the fuel dielectric constant, and hence, the composition of the fuel mixture flowing through the sensor to the engine.
One problem associated with alcohol-gasoline fuel mixtures, that has not heretofore been addressed, is that of fuel contamination. Alcohol based fuels, especially those containing methanol, have the capacity to dissolve large quantities of water and other ionic contaminants due to the relatively large dipole moment associated with alcohols. In sufficient amounts, these dissolved fuel contaminants can cause the failure of components in the fuel supply system such as the fuel pump, fuel filter, fuel injectors, and the fuel composition sensor.